ID #1880

When microtubules depolymerize, because of the low concentration of GTP-bound tubulins, the tubulins on the microtubule fall off. Do the depolymerized free tubulins in return increase the concentration of the tubulins in the solution and thus trigger polymerization after a while again? If they do, do they just somehow change from GDP-bound tubulins to GTP-bound?

When they fall off, if they were ready to be added back to a microtubule, they would in fact increase the local concentration of available tubulin. But as you accurately pointed out in your message, it is GTP-bound tubulin that gets added to the microtubule, but it's GDP-bound tubulin that falls off. So until an enzyme comes around and swaps out that GDP for a fresh GTP, that tubulin dimer is not able to be added to the chain, and does not affect the local concentration of GTP-bound tubulin.

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